Electron Microscopy of Amoeba proteus*†

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Abstract
SYNOPSIS. Thin sections of Amoeba proteus, fixed in osmium tetroxide and embedded in methacrylate, were examined in the electron microscope. The fine structure of various protoplasmic components is described. The plasmalemma, or cell membrane, varies in thickness and structure. These variations may be due to variations in physiological state, or they may be due to differences in preparation. Along its cytoplasmic edge is always present a definite line approximately 0.01 to 0.02 μ thick. The mitochondria, or beta granules, exhibit a structure similar to that of the mitochondria of several other protozoa and comparable to that of the mitochondria of other animals. In definite association with the membrane of the food vacuole are dense, rounded particles which in size are below the limit of resolution of the light microscope. Such dense particles are much less frequently present in the hyaloplasm and in association with the plasmalemma. A possible relationship to the neutral red granules associated with food vacuoles of Paramecium is suggested. The contractile vacuole possesses a thin membrane surrounded by a much thicker circum‐vacuolar zone of irregular strands which may form a three‐dimensional network around the membrane. This may represent the contractile element of the vacuole. A single layer of mitochondria is closely apposed to the circum‐vacuolar zone. Many small vacuoles and irregular vesicles are present throughout the cytoplasm. At times there occur groups of small, thin‐walled vesicles, which may correspond to an endoplasmic reticulum. The nuclear envelope consists of a thick inner porous layer and a thinner outer layer that is continuous yet is marked by the presence of numerous small annuli, each apparently surrounding a pore. In its structure, this outer layer appears to correspond to the entire nuclear envelope of many other cell forms.